Pneumatics Differences

VEX V5 General Discussion
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Hi all — I’m learning about pneumatics. I have learned about the two types:

  1. A single acting cylinder pushes out with air, but pulls back with a spring.
  2. A double acting cylinder pushes out with air, and pulls back with air.

I understand that neither is “better”, they just have different uses. Depending on your application, one may be better than another. What I’m wondering is - what type of applications are each type used for?

Thanks!

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simply put,

a single acting is if you want force in only one direction, and it uses less air

a double acting is if you want force in two directions, and it uses twice as much air as a single acting cylinder (if not regulated)

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So like if I wanted a shooting mechanism, I’d use a single acting?

For double, an intake roller that goes both ways?

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pneumatics are linear motion, and can only go a couple of inches, if you want an intake, use motors, if you want a claw, use pneumatics

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Well, double acting are actually better than single acting in most scenarios. Even if you only want to use air in one direction, double acting cylinders will allow you to chose that direction, and will allow you to chose the method of return, reducing the force acting against the stroke to the minimum, making it overall stronger.

The only advantage I can think of with single acting is that they have a slightly smaller size. But not by very much, and that might not be an advantage depending on the application.

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Single acting pistons are actually longer than double acting pistons.

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not according to the info on the product page:

it gives the single acting lengths as 5.5" compressed to 7.5" extended, and the double acting lengths as 6.125" compressed to 8.25" extended.

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we used to use a double acting piston on our claw, acting in one direction, retracting with rubber bands, but now we use two single actings, and they move the claw much much further.

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interesting. I only have double acting cylinders, does someone with both types want to measure the lengths to compare against the numbers vex provides?

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Both single acting cylinders, and double acting cylinders, have the same stroke of 2". Physically, the single acting the cylinder is a little longer because they have to make room in the cap for the return spring, but this does not change the 2-in stroke

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so are the numbers on the product page incorrect then?

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12

The only reasons to use single action are cost and availability

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Yeah, there’s probably a typo there somewhere. 6-1/8 to 8-1/4 would be 2-1/8 in stroke

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and to conserve pressure

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A double action piston cylinder can be driven from just one end, which uses the exact same amount of air as a single action. If you go that route, you will need to us rubber bands or gravity to push or pull the cylinder in the opposite direction. For a while we were using double action cylinders on our front gripper with rubber bands just pulling them back together.

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